Treatment of hydrocarbons



Feb. 29, 1944. v. MEKLER 2,342,881

TREATMENT OF HYDROCARBONS Filed Feb. 20, 1945 Caudefl'acil'dmigg INV ENTOR Mahler ATTORNEY use of catalysts.

Patented Feb. 29, 1944 TREATMENT F ROQARBONS Valentine Mekler, JacksonHeights, N. Y... assignor to The Lummus Company, New York, N. Y., acorporation of Delaware Application February 2@, 1343, Serial No.476,568

3 Claims. (Ci. 260-6735) This invention relates to the treatment ofhydrocarbons and particularly to a process of converting hydrocarbons inthe vapor phase whereby a high yield of high-octane motor fuel isobtained. More specifically, this invention relates to a multistageprocess for converting relatively heavy predominantly parafiinichydrocarbons into lighter predominantly aromatic hydrocarbons, in whichprocess a combination of thermal and catalytic cracking, cyclizing anddehydrogenating operations is so utilized that the parafiinichydrocarbons are selectively and progressively converted into aromatichydrocarbons suitable for use in a high-octane motor fuel. Thisapplication is a continuation in part of my prior co-pendingapplication, Serial No. 280,961, filed June 24, 1939.

It is well known to the art to convert heavy hydrocarbons intogasoline-like hydrocarbons in the vapor phase under suitable conditionsof temperature and pressure, either with or without the It is customaryto pass the hydrocarbon vapors through a conversion unit, in which theyare subjected to one set of conversion conditions of temperature,pressure, and time of contact. As a result, only certain constituents ofthe complex hydrocarbon mixture undergo favorable reactions, theremainder of the hydrocarbons either being overconverted or remainingunchanged, with a resultant loss in the yield and the quality of theflnal product. In addition, uncondensable gas and carbon may be formedin such quantities as to adversely affect the ultimate yield of thefinished product.

It is also well known that each particular hydrocarbon has its ownspecific optimum conversion conditions and that the maximum yield ofdesirable converted product is not obtained if the hydrocarbon is notsubjected to these conditions. Further, it is known that, for paraffinichydrocarbons, the optimum temperature for cracking decreases with anincrease in the molecular weight of the hydrocarbons treated. Forinstance, it has been determined that the approximate decompositiontemperature for ethane is 1550 F. and that for hexadecane at the samepressure is about 875-930 F. In addition, it has been found that thestability of hydrocarbons of the same molecular weight at crackingtemperatures increases from parafilns to aromatics as follows:paraflins, olefines, diolefines, naphthenes, and aromatics.

It is the principal object of my invention to subject rc atively heavyparaffinic hydrocarbons to a multistage conversion process, in which thehydrocarbons are selectively and progressively converted into aromatichydrocarbons of high octane rating.

Another object of my invention is to efiect a selective conversion ofrelatively heavy paraiflnic hydrocarbons by passage of such hydrocarbonsthrough a series of conversion stages, each stage being comprised of aheating unit and a catalytic conversion unit, the heating unit servingprimarily to heat the vapors of the hydrocarbons to a predeterminedtemperature suitable for the selective conversion of a particular groupof the hydrocarbons in the accompanying catalytic unit, the catalyticconversion unit being maintained at the predetermined temperature forthe conversion. Although the heating unit serves primarily to raise thetemperature of the hydrocarbon vapors undergoing treatment, it will beunderstood that some cracking of the hydrocarbons may also take placetherein.

A further object of my invention is to control the conversion conditionsin the catalytic units throughout the process so that the predominantreaction in the first stages is the selective conversion of the heavierparamns into olefines and lighter parafiins, in the intermediate stagesthe selective conversion of the lighter parafilns into olefines and ofthe olefines into alicyclic compounds such as cyclo-olefines, and in thelatter stages the selective conversion of any remaining olefines intoalicyclic compounds and of the alicyclic compounds into aromatics.

Further objects and advantages of my invention will be apparent from thefollowing description of a preferred form of embodiment thereof taken inconnection with the attached drawingj;

illustrative thereof, such drawing being a flo sheet in accordance witha preferred form of e bodiment of the invention.

In accordance with the present invention, the relatively heavy paramnichydrocarbons are first vaporized, and all the vapors are then passedthrough a series of conversion stages, each comprised of a heating unitand a catalytic unit and each maintained at a predetermined temperaturewhich is favorable for the selective conversion of a particular group ofsuch hydrocarbons. Accordingly, the hydrocarbons which are convertedunder the mildest conditions are acted upon first. and then thosehydrocarbons more difllcult to convert are successively acted upon byreason of the gradual increase in the severity of the conditions towhich the hydrocarbons are subjected.

and easily changed to take care of a wide range of starting stocks andto provide a variety of end products.

Although any number of stages, which may be necessary to effect thedesired conversion, may be used, the inventionwill be described asembodied in a three-stage system, in which the first stage serves toconvert the heavier parai'flns into olefines and lighter parafllns, thesecond stage serves to convert the lighter parafilns into additionalolefine and the oleflnes into alicyclic compounds such ascyclo-oleilnes, and the third stage serves to convert the remainingoleflnes into cyclo-olefines and the cycl-.-oleflnes into aromatics.

In accordance with a preferred form of embodiment of my invention, acrude oil is charged to i'ractionating tower Ill at i2 after it has beensuitably preheated in heater ll Tower ll may be of any conventional typeof fractionating apparatus such as a bubble plate tower suitable forseparating the crude oil into a plurality of fractions. An overheadfraction is taken of! at I. and is condensed at ll, part of thecondensate being returned as reflux at 20 and the remainder beingremoved at 22 as straight-run gasoline. Side streams such as naphtha,kerosene, light gas oil, and heavy gas oil are removed at 23, 2!, 26,and 21, respectively. A bottoms stream is removed from the tower at 23.

Each of the above side streams may be subiected to my multistageconversion process if desired. For convenience, however, my inventionwill be described in connection with the treatment of the light gas oilside stream, it being understood that the invention is equallyapplicable to the treatment of any or all of the other side streams.

The light gas oil side stream, which is removed at 23, is passed by pump28a to a multistage conversion system indicated generally at 29, 30.and' ti. Each of these stages consists of .a heating coil indicated at32, 33, and 33 and a vapor-bhasecatalytic conversion unit indithecatalyst is maintained in situ, but a catalyst chamber in wh ch bothvapors and catalyst flow through in continuous streams is preferred.

In the catalyst chamber 35 (conventionally shown), the vapors. enteringat 38. preferably flnw u wardly countercurrent y to the. catalyst, whichis moved downwardly through the chamber in a continuous stream bysuitable means (not shown). The catalyst. which may be of any typesuitable for eilecting the desired conversion, is fed to the chamber at39 and is withdrawn at 40. The spent catalyst may be reactivated orthrown away as desired. The vapors which leave catalyst chamber 35 nearthe top consist primarily of oleflnes and light paramns. Preferably,catalyst chamber is equipped with heatin means (not shown) so that thetemperature of the vapors therethrough is maintained at the properlevel.

The partially converted vapors from chamber 35 are passed through coil33, in which they are heated to a temperature normally higher than thatmaintained in the previous stage, which is suitable for the conversionin catalyst chamber 33 of the light paramns into oleiines and thecyclization of the oleflnes into alicyclic compounds such ascyclo-oleilnes. Cracking of the hydrocarbons may also occur in coil 33,but again undesirable side reactions are held to a' minimum. The vaporsleaving coil 33 may pass directly to catalyst chamber 36 in line II, orthey may be diverted in whole or in part through line I! to tarseparator 43, where any tar inadvertently formed in previous operationsmay be knocked out and removed at 44. From the tar separator the vaporspass to chamber 33 through line ll. Catalyst chamber 33 is similar inoperation to chamber 33: hydrocarbon vapors enter at 43, flowingcountercurrently to the catalyst, which is fed in at I. and withdrawn at41. The vapors leaving chamber 30 at I are composed mainly of oleiinesand cyclo-olefines and may contain unconverted light paraflins.

These vapors are then passed to the third conversion stage. in whichthey are heated in coil 34 preferably to a higher temperature than thatmaintained in stage 30 before they are introduced into catalyst chamber31 at 53'. Tar separator may also be provided for removal oftar at 5|.

In this last stage the hydrocarbons are preferably heated to atemperature sumcient to convert into oleflnes light paramns which mayhave been unconverted in the previous stages. Usually this temperatureis so high that the vapors cannot be subjected to the action of thecyclizing and dehydrogenating catalyst in chamber 31 without deleteriouseflect on the catalyst. In this case the vapors issuing from coil 34 arecooled in cooler ila to a temperature such that the catalyst is notadversely affected: Catalyst chamber" is also preferably operated in the5 same manner as the other catalyst chambers with the catalyst fed in atI! and removed at 58.

The conversion products leaving the final conversion stage are passed tofractlonating tower 88, also preferably a bubble plate tower,'in'whichthe vapors are fractionated into a high-octane gasoline, removed asoverhead at 63, and a bottoms, withdrawn at 82. The overhead iscondensed at 63, reflux is returned to the tower'at N, and high-octanegasoline is withdrawn at 65.

This high-octane gasoline may be subjected to any desired stabilizingand refining operations which may be necessary to obtain aspeciilcflnished product. The bottoms withdrawn at 62 may be recycled asby means of line ll for admixture with the charge to pump 26a. If thebottoms has such a compositionthat recycling cannot be carried out, itmay be withdrawn at It and treated in any desired fashion, or it may beremoved to storage.

If desired, conversion products from othermultistage conversion systemsmay be commingled with the vapors flowing in line 68 as at 10 and II,and the mixture passed to tower 58 at 12.

Although provision is made at 43 and 50 for the removal of any tarpreviously formed, it will be clear from the description and the drawingthat substantially the entire hydrocarbon charge is subjected to eachstage of the conversion system. Furthermore, with the type of catalystchamber described, it may be found that separators 43 and 50 are notneeded since any tar formation will be deposited on the catalyst andcontinuously removed.

Conversion conditions differ in each stage so that optimum conversion ofthe hydrocarbon charge may be efiected. The degree of heating to whichthe hydrocarbon vapors are subjected varies from stage to stage as wellas the temperature, the time of contact, and the catalyst in thecatalytic unit. In addition, for charging stocks of different types,these conditions also .vary.

In the form of embodiment described, in the first stage the main objectis to convert the heavier parafiin hydrocarbons into olefines andlighter parafiins. For this purpose, a catalyst suitable for splittingheavy hydrocarbons is used. Such catalyst may be selected from theoxides of aluminum, nickel, cobalt, molybdenum, and chrmium, forexample, and may be in admixture with silica gel, activated alumina,pumice, and the like; or it may comprise any other substance suitablefor eifecting a splitting reaction of the type desired. The temperaturein this stage may range from 600 to 750 F.

The second stage has for its main object the conversion of the lighterparaflins not affected in the first stage into olefines and thecyclization of the olefines into alicyclic compounds such ascyclo-oleflnes. Although a catalyst similar to the one used in the firststage may be employed in the second, the temperature level is higher,ranging from 750 to 950 F., and the contact time is lower.

In the third stage, the main object is the cyclization of the remainingolefines into cycloolefines and the dehydrogenation of the cycloolefinesformed in the previous stage into aromatic hydrocarbons. The catalystemployed may be one of the metallic oxides which are suitable foreffecting the cyclization of olefines into cyclo-olefines and thesubsequent dehydrogenation thereof into aromatics. For such purpose,chromium oxide, preferably specially prepared so as to increase itsactivity, may be used; desirably, however, this oxide is used inadmixture with other catalytic materialssuch as alumina, nickel, andoxides of such metals as iron, molybdenum, tin, tungsten, and vanadium.Other oxides such as zinc oxide are also suitable. Heavy metal salts mayalso be used as the catalyst; among these may be mentioned themolybdates and tungstates of nickel, vanadium, chromium, iron, andtitanium, as well as other salts including chromates such as zincchromate and sulfides such as zinc sulfide. The temperature in theheating coil ranges from 950 to 1350 F., but a temperature somewhatlower, within the range of 900 to 1000 F., is maintained in the catalystchamber so that the catalyst is not subjected to too high temperatures.

Although in each stage of this selective conversion process, reactionsof cracking, cyclization, dehydrogenation, polymerization, and the likeare taking place to some extent simultaneously, the predominant reactionin each stage is so controlled by the temperature, contact time, andcatalyst used that undesirable side reactions are held to a minimum. Bymeans of this control over temperature, contact time, and catalyst, ineach stage a desired selective conversion of the hydrocarbons undergoingtreatment takes place. In each stage the reactions are controlled sothat stable intermediate hydrocarbons are formed; and, by means of theheating step, the hydrocarbons are prepared for the next step ofselective catalytic conversion. Although thermal cracking does occur tosome extent in the various heating coils, the conversion is accomplishedprincipally by catalytic action.

Since the main part d of the conversion reactions is catalytic innature, high pressures are not necessary to carry on the operation ofthe process. Pressures only slightly above atmospheric need be employed,the pressure being at least sufiicient to overcome the pressure dropthrough the apparatus. The yield of gasoline hydrocarbons, however, ishigher than that of single-stage catalytic conversion processes, and theend point of the product obtained is also under substantially bettercontrol.

The problem of catalyst reactivation is taken care of outside of thesystem since spent catalyst is continuously removed from the bottom .ofthe catalyst chambers while fresh catalyst is supplied at the topthereof. Any carbon or tarry materialthat deposits on the catalyst doesnot effectively alter the activity of the catalyst with respect to theparticular reaction since the catalyst is continuously withdrawn fromthe chambers.v Similarly, sulfur poisoning does not afiect the catalystactivity to an appreciable extent.

While I have described a preferred form of embodiment of my process, Iam aware that there may be modifications thereto; and I, therefore,desire a broad interpretation of my invention within the spirit andscope of the description herein and of the claims appended hereinafter.

I claim: I

1. The process of converting relatively heavy predominantly parafiinichydrocarbons into relatively light predominantly aromatic high-octanegasoline hydrocarbons, which comprises vaporizing the pa'raifinichdrocarbons and heating the resulting vapors to a temperature of 600 to750 F., passing the heated vapors into contact with a catalyst selectedfrom the group consisting of the oxides of aluminum, silicon, nickel,cobalt,

molybdenum, and chromium primarily to crack the heavier paraflinichydrocarbons into olefinic hydrocarbons and lighter paramnichydrocarbons, heating the partially converted vapors to a temperature of750 to 950 F., passing the heated vapors into contact with a catalystselected from the group consisting of the oxides of aluminum, silicon,nickel, cobalt, molybdenum, ancl chromium primarily to crack the lighterparaffinic hydrocarbons into olefinic hydrocarbons and to partiallycyclize the oleflnic hydrocarbons into cyclic hydrocarbons, the time ofcontact of the vapors with the catalyst in this second cracking stagebeing less than that in the first cracking stage, then further heatingthe vapors to a temperature of 900 to 1000 F., passing the heated vaporsinto contact with a catalyst capable of cyclizing olefinic hydrocarbonsinto cyclic hydrocarbons and dehydrogenating cyclic hydrocarbons intoaromatic hydrocarbons primarily to cyclize the remaining oleiinichydrocarbons into cyclic hydrocarbons and to dehydrogenate the cyclichydrocarbons into aromatic hydrocarbons, and tractionating the convertedvapors to obtain the desired high-octane aromatic gasoline fraction.

2. The process 01' converting relatively heavy predominantly paraiiinichydrocarbons into relatively light predominantly aromatic high-octanegasoline hydrocarbons, which comprises vaporizing the parafllnichydrocarbons and heating the resulting vapors to a temperature of 600 to750 F., passing the heated vapors into contact with a catalyst selectedfrom the group consisting of the oxides of aluminum, silicon, nickel,cobalt, molybdenum, and chromium primarily to crack the heavier par 10hydrocarbons into oleflnic hydrocarbons an lighter parafllnichydrocarbons, heating the partially converted vaporsto a temperature of750 to 950 F., passing the heated vapors into contact with a catalystselected from the group consisting of the oxides of aluminum, silicon,nickel, cobalt, molybdenum, and chromium primarily to crack the lighterparafllnic hydrocarbons into oleflnic hydro- 25 carbons and to partiallycyclize the olefinic hy-' crack any remaining light paraflinichydmcarbons into oleiinic hydrocarbons, lowering the temperature 0! thevapors to about 900 to 1000' It, passing the vapors thustemperature-conditioned into contact with a catalyst capable ofcyclizing oleflnic hydrocarbons into cyclic hydrocarbons anddehydrogenating cyclic hydrocarbons into aromatic hdrocarbons primarilyto cyclize the remaining olefinic hydrocarbons into cyclic hydrocarbonsand to dehydrogena'te the cyclic hydrocarbons into aromatic hdrocarbons,and fractionating the converted vapors to obtain the desired high-octanearomatic gasoline fraction.

3, The process as claimed in claim 2, in which the predominantlyparafllnic hydrocarbons comprise a fraction boiling within the range ofgas oil.

VALENTINE

